How to Build a Dinosaur (7 page)

One of the first collectors in the area of Garfield County was Barnum Brown of the American Museum of Natural History, the man who identified and named the Hell Creek Formation. He arrived shortly after Arthur Jordan, a remarkably enterprising man, who had emigrated from Scotland as a boy, and founded the town of Jordan, which began as a post office in 1899.

In 1902 Brown was sent to explore the Hell Creek area by Henry Fairfield Osborn, the paleontologist who would become president of the museum in 1908 and preside over the glory days of the museum’s fossil collecting. This commission meant that Brown was well on his way to becoming one of the most successful and best-known collectors of dinosaur fossils. He had already been fossil hunting in Wyoming and had been told by Hornaday of fossils weathering out in the badlands near Jordan.

On his first trip there he found fossils of an unknown dinosaur that Osborn christened
Tyrannosaurus
. In 1908 he found a more complete specimen here that included a well-preserved skull.

The Hell Creek Formation has continued to attract fossil hunters of all sorts, academic and professional, and over the years has produced more than its share of tyrannosaurs and other dinosaurs. It has been studied in three states by paleontologists from all parts of the country. The reasons are those that I have already described, the exposed and weathered badlands. The worse the country, the more tortured it is by water and wind, the more broken and carved, the more it attracts fossil hunters, who depend on the planet to open itself to us. We can only scratch away at what natural forces have brought to the surface.

 

 

So, like many others before us, our team from the Museum of the Rockies attacked the Hell Creek rocks. Although the formation is known for being rich in
T. rex
fossils, that was not what attracted us initially, although it certainly did pay off. We chose Hell Creek because it is not only rich in fossils but richly varied in the kinds of fossils it yields. Other sites have lots of one thing, like many duck-billed dinosaurs. Hell Creek has a wide range of dinosaurs, other reptiles, mammals, and plants.

We planned a dig that would take a snapshot of this ecosystem at one location, focusing on as narrow a time frame as possible. No biologist would suggest that a living organism can be understood in isolation. Its living conditions, its food sources, predators, and countless other factors in its environment affect how it lives and how it has evolved. A leech makes no sense unless one knows about its environment and the creatures it feeds on.

Near Choteau, in the Two Medicine Formation, where we found the first nesting grounds of dinosaurs in the late seventies, we had managed to get a remarkably detailed record of what seemed to be one nesting season so many millions of years ago.

We wouldn’t be able to be quite so precise at the Hell Creek Formation, but we did hope to find fossils of many dinosaur species and many animals and turtles and plants and pollen and mollusks. I recruited a dozen colleagues, senior scientists at different institutions, like Bill Clemens at Berkeley, who studies mammals; Joe Hartman, in North Dakota, whose specialty is clams and snails; and Mark Goodwin, also at Berkeley, a fellow dinosaur paleontologist. I also found private funding for what promised to be an expensive few years. We had geologists, students, plant people, Mary Schweitzer for biochemistry—all working independently toward the same goal. In the summer we would have as many as fifty people in the field prospecting and excavating what they found. We are still cataloging and studying our finds.

Even though we were set up to look for many different fossils, and we did find a variety of species, the formation is so rich in
T. rex
that in 2000 alone we found five specimens. The one that turned out to be most intriguing for research also turned out to be the hardest to get out of the ground.

On the morning of June 28, Bob Harmon, a native Montanan who was in charge of my crew at the dig, set out prospecting. He took a boat to a satellite camp and walked about a mile and a half, looking for good sites. He stopped for lunch by a cliff. After lunch he looked up on the side of the cliff and saw what seemed to be an exposed fossil bone. He scrambled up about twenty feet to a ledge, but he couldn’t reach the bone, so he made his way back down the cliff and walked to the satellite camp on the shore of the reservoir.

If it were me, I would have gone back and got myself a graduate student. But Bob didn’t get a graduate student. He got a folding chair. He scrambled back up the twenty-foot cliff with the chair. On the ledge he piled up some rocks, put the folding chair on top of the rocks, climbed up on the chair, and took photographs.

He spotted two other bones. That made three, and by my rule of thumb, three different bones from what seems to be the same creature mean an animal that died and was preserved in one place. Over millions of years wind, rain, and rivers scatter most bones. Finding three together is a sure sign that more from that same animal are under the surface.

The problem was that this hint of a skeleton was at the base of a forty-foot cliff, rising up from the shelf of the twenty-foot rise Bob had climbed up. I wanted to see more, but my knees have long since resigned from that sort of climbing. I brought in Nels Peterson, an engineering student and a rock climber. He brought several other climbers.

They set up a belaying station above the cliff and lowered people down. Then they lowered small jackhammers down to the climbers to begin work, to begin what turned into years of backbreaking work. Eventually, we found both hind legs, both femurs, one tibia and a fibula and a piece of jaw, and a bunch of bones going back into that cliff. All told, we collected about 50 percent of the skeleton. It was a tyrannosaur, and as I said earlier, we called it B. rex, for Bob.

That skeleton has led us farther into the past than any other. Not in time, but in the detail and depth of our understanding. To be sure, it is the oldest
T. rex
skeleton, at sixty-eight million years, but dinosaurs go back more than two hundred million years, the origin of life more than three billion. Many, many fossils are older, but few have been studied like B. rex.

It began with the excavation, which at the time seemed like building, or perhaps taking apart, the pyramids. We, and by we I mean they, spent three years to free the bones—three years of many graduate students and numerous jackhammers, big and small.

Once we could see the bones, the job was still far from done. The fossils had to be jacketed with plaster, and since the site was so inaccessible, the enormous plaster-jacketed loads had to be lifted out by helicopter. One jacket, including the femur, was simply too big for the helicopter, so it had to be broken in two. That small fact—that we had to break the jacket in two—is what led us to look at the tissue inside the bone.

A PREGNANCY TEST FOR
T. REX

By the help of Microscopes, there is nothing so small, as to escape our inquiry; hence there is a new visible World discovered to the understanding.

—Robert Hooke

 

 

W
hen we broke the plaster cast of the B. rex femur in two so that a helicopter could lift it from the site of the demolished cliff, we exposed extremely well-preserved tissue from the interior of a fossil that had lasted sixty-eight million years. It was that long ago that B. rex, an ovulating
Tyrannosaurus,
had moved through the lush thickets and forests of a delta fed by several winding rivers. She had hatched, and spent sixteen to twenty years growing to maturity before she mated.

Whether this was her first mating or not, we can’t tell. Perhaps she died without offspring. Perhaps she had shepherded a clutch of eggs to hatching before. From the point of view of the present it may seem poignant that B. rex was living near the end of the 140-million-year reign of dinosaurs on earth, as if she were one of the last of her line. But she was only near the end in the terms of geological time. There were three million years to go before the end of the Cretaceous.

She died of unknown causes, but we do know that her burial was quick because her skeleton was well preserved, most of it, including the femur, encased in the tons of rock we had to remove with jackhammers. In fact, this femur was still in its matrix of rock inside the plaster jacket. Where we broke the jacket the bone had not been coated with any protective chemical, which is the common process for fossils found exposed to the elements. We paint them with a chemical preservative so that they will not disintegrate further, at least in external form and shape. But preserving the bone from further damage from water and weather may damage it for laboratory analysis, because the preservative can seep in and alter the very chemicals we are looking for.

Like so much in science, there was a bit of luck involved. Bad luck for the crew that had to break the cast open, and good luck for Mary Schweitzer, the beneficiary. I am fairly willing to break open fossils or cut thin sections to view under a microscope. I’m in favor of pulverizing some fossil material for chemical analysis. But without this unplanned break I doubt that we would have taken the B. rex femur back to the museum and snapped it in two. B. rex was a superb and hard-won fossil skeleton. Mary was looking for well-preserved fossil bone that had not been chemically treated, and she and I both had hopes for what she might find. But I’m not sure I would have picked this particular femur.

But necessity can be the mother of research material as well as invention. And when we saw the inside of the femur, and smelled it—fossils from Hell Creek tend to have a strong odor, which may have something to do with the organic material preserved—it was clear that this was prime material for Mary.

So we packed the bits of
T. rex
thighbone up and Mary took them with her to North Carolina State University, where she was starting her first semester as an assistant professor. For the previous ten years she had been studying and working at the museum, digging deep into the microscopic structure of fossilized bone tissue, and now she was leaving just about the time we were returning from the field season in August.

Mary snapped up the fragments. “I packed up the box,” she said, “and brought it with me to Raleigh, and as soon as we got there my technician, Jen [Jennifer Wittmeyer]—I could not have done any of this without her—she said, ‘What do you want to do first?’ I said I had plans for the
T. rex
bone. So we pulled out the first piece of bone from the box and I said, ‘My gosh, it’s a girl and its pregnant.’

“I picked it up and I turned it over and the inside surface was coated with medullary bone. It’s a reproductive tissue that’s only found in birds. Birds are constrained by the fact that they have very thin bones, which are an adaptation for flight, and they make calcified eggshells,” she said. There is not a whole lot of calcium available from the skeletal bones because they are lightweight, but birds need calcium for eggshells. “So,” she said, “they developed a reproductive tissue that is laid down with the first spike of estrogen that triggers ovulation.”

It was easy to spot, since it looked very different from other types of bone. Medullary bone is produced rapidly, has lots of blood vessels, and has a kind of spongy, porous look and feel to it. Since birds are dinosaurs, and
T. rex
is in the family of nondinosaurs from which birds claim descent, the presence of medullary bone made sense. Paleontologists had hoped to find medullary bone in dinosaur fossils, but they had not yet. If she was right in her snap judgment, this was not only scientifically important but a treat for all of us who love dinosaurs—a girl tyrannosaur.

And that is how the second excavation of B. rex began. The first, the old-fashioned kind, was to dig into the rock to free the fossil bone. The second excavation, of a sort that will mark a sea change in paleontology as it becomes more common, was to dig into the fossil itself, not with dental pick and toothbrush, but with the tools of chemical and physical analysis. Most of our current knowledge of dinosaurs and other extinct animals consists of the fruits of first excavations. I am not undervaluing this knowledge. In fact, it is almost impossible to overstate its value.

The work of traditional paleontology has produced a record of evolution on earth. The great skeletons that tower over museum exhibition halls are flashy, but they are mere points of data in the grand accumulation of knowledge. Fossils that show how jaws evolved or when a toe moved, or an opening in a skull appeared, are equally as important in mapping not just the existence of the past, but the process of evolution, and eventually the laws that govern its progress.

But there are now new means of tracing the past and some paleontologists are using them, although they don’t seem to spread as fast as they might. As long ago as 1956 Philip Abelson reported amino acids in fossils more than a million years old. In the 1960s and 1970s other scientists pushed for the importance of molecular biology for scientists who study the past. Bruce Runnegar of UCLA summed up a new view at a 1985 conference when he said, “I like to take the catholic view that paleontology deals with the history of biosphere and that paleontologists should use all available sources of information to understand the evolution of life and its effect on the planet. Viewed in this way the current advances being made in the field of molecular biology are as important to present-day paleontology as studies of comparative anatomy were to Owen and Cuvier.”

Change does not come easy, however. Scientific disciplines are more like barges than speedboats, slow to turn in a new direction. This is as true for scientists who study dinosaurs as for any others. And there are significant obstacles to moving in a new direction. For one thing, dinosaur fossils are so old that recovering biological materials from them has been a major challenge.